Nickel complexes oxidative addition reactions

Lin BL, Clough CR, Hillhouse GL (2002) Interactions of aziridines with nickel complexes oxidative-addition and reductive-ehmination reactions that break and make C—N bonds. J Am Chem Soc 124 2890-2891... 

Substantially more work has been done on reactions of square-planar nickel, palladium, and platinum alkyl and aryl complexes with isocyanides. A communication by Otsuka et al. (108) described the initial work in this area. These workers carried out oxidative addition reactions with Ni(CNBu )4 and with [Pd(CNBu )2] (. In a reaction of the latter compound with methyl iodide the complex, Pd(CNBu )2(CH3)I, stable as a solid but unstable in solution, was obtained. This complex when dissolved in toluene proceeds through an intermediate believed to be dimeric, which then reacts with an additional ligand L (CNBu or PPh3) to give PdL(CNBu )- C(CH3)=NBu I [Eq. (7)]. 

The starting material is an 18 electron nickel zero complex which is protonated forming a divalent nickel hydride. This can react further with alkenes to give alkyl groups, but it also reacts as an acid with hard bases to regenerate the nickel zero complex. Similar oxidative addition reactions have been recorded for phenols, water, amines, carboxylic acids, mineral acids (HCN), etc. 

The mechanism of the ZnBr2-assisted, nickel-catalyzed Reformatsky reaction has been discussed [540]. The reaction involves the electroreduction of a Ni(II) complex to a Ni(0) complex, oxidative addition of the a-chloroester to the Ni(0) complex, and Zn(II)/Ni(II) transmetallation, leading to an organozinc Reformatsky reagent. Most recently, the Reformatsky reaction... 

Some Examples of Oxidative Addition Reactions to Nickel(0) Complexes 31... 

Oxidative addition reactions to nickel(O) complexes are another well-developed synthetic method which affords mono and bis alkyl and aryl compounds (equation 148).1232-1239 The oxidative addition of a, ar -dichloro-p-xylene to [Ni(QjH4)(PPh3)2] gives the dinuclear nickel(II) complex t(PPh3)2ClNi(CH2C6H4CH2)NiCl(PPh3)2].124 ... 

The nickel-catalyzed transformation of aromatic halides into the corresponding nitriles by reaction with cyanide ions is reported. Both tris(triarylphosphine)nickel(0) complexes and tY2ins-chloro( aryl )bis( triarylphosphine )nickel(II) complexes catalyze the reaction. The influence of solvents, organophos-phines, and substituents on the aromatic nucleus on catalytic cyanation is studied. A mechanism of the catalytic process is suggested based on the study of stoichiometric cyanation of ti3ins-chloro(aryl)bis(triphenylphosphine)nickel-(II) complexes with NaCN and the oxidative addition reaction of Ni[P(C6H5)3]s with substituted aryl halides. 

Therefore it seems reasonable to assume that cyanation of aryl halides involves two fundamental processes oxidative addition of the tris(triphenylphosphine)nickel complex on the aromatic halide (Reaction 2) and cyanation of the arylnickel(II) complex 1 (Reaction 8). A further proof of the validity of this scheme is that both Ni[P(C6H5)3]3 and arylnickel (II) complexes 1 have an equal catalytic activity, these latter being intermediates of the catalytic process. Recent studies (22) on the influence of substituents on the aromatic halide in the oxidative addition reaction with Ni[P(C6H5)3]3 have given the results shown in Figure 4. 

Their advantage over other types of dendrimers is their straightforward synthesis and, most importantly, their chemical and thermal stabilities. Two distinct steps characterize their synthesis a) an alkenylation reaction of a chlorosilane compound with an alkenyl Grignard reagent, and b) a Pt-cata-lyzed hydrosilylation reaction of a peripheral alkenyl moiety with an appropriate hydrosilane species. Scheme 2 shows the synthesis of catalysts Go-1 and Gi-1 via this methodology. In this case, the carbosilane synthesis was followed by the introduction of diamino-bromo-aryl groupings as the precursor for the arylnickel catalysts at the dendrimer periphery. The nickel centers of the so-called NCN-pincer nickel complexes were introduced by multiple oxidative addition reactions with Ni(PPh3)4. 

New nickel-benzyne complexes (143-147) have been prepared by reaction of o-dihaloarenes with Ni(COD)2 in the presence of a trialkylphosphine followed by reduction of the oxidative addition product with either Li or 1% Na/Hg in ether [e.g., Eq. (23)]. The oxidative addition reaction depends on the nature of substituents on the arene and fails to occur when strong electron-donating groups are present. Based on NMR and mass spectrometry (MS) data, the new complexes were formulated as monomeric. It had been... 

The acidification of H2 may also be involved in hydrogenase action, where H2 is beheved to bind to an Fe(II) center. Isotope exchange between H2 and D2O is catalyzed by the enzyme see Nickel Enzymes Cofactors Nickel Models of Protein Active Sites Iron-Sulfur Proteins). Similar isotope exchange can also occur in H2 complexes. Oxidative addition to give a classical dihydride is also a common reaction. [W(H2)(CO)3(PCy3)2] is in equilibrium with about 20% of the dihydride in solution. This can lead to subsequent hydrogenolysis of M-C bonds as in the case of a cyclometallated phenylpyridine complex of Ir(III). ... 

Ethylene (tert-phosphine) complexes of zero-valent nickeP and platinum have been known for years. Analogous palladium complexes can be synthesized along the same lines as those reported for the nickel compounds, using ethoxy-diethylaluminum(III) as the reducing agent in the presence of ethylene. These palladium-ethylene complexes may serve as starting materials for oxidative addition reactions, since the ethylene ligand is loosely bonded. ... 

In Section II,C, the oxidative-addition reaction of protonic acids to low-valent complexes was discussed. This reaction can lead to formation of either the hydro complex or to the bis complex of the conjugate base. Both of these reactions have been reported for the addition of silanes to low-valent complexes of the nickel triad (73, 74). It is to be expected that the nature of the product will depend on the strength of the acid HX and the trans influence of the conjugate base X. If the acid is strong and the conjugate base has a large trans influence, then it would be anticipated... 

Nickel(O) complexes undergo oxidative addition reactions with alkynes to give nickelacyclopentadienes and also react under certain conditions with carbon dioxide or isocyanates to form oxanickelacyclopentenones (87) " or azanickelacyclopentenones (88) (Scheme 30). In both cases the chelating basic ligand TMEDA (tetramethylethylenediamine) influences the reaction strongly. 

Not only noble metal complexes, but also nickel complexes undergo oxidative addition reactions. Fahey found that a variety of vinyl and aryl halides react with (R3P)2Ni(C2H4) to form a stable carbon-metal o-bond 24). Forex-ample, tetrachloroethylene affords /ran. -chloro(trichlorovinyl)bi s(triphenyl-phosphine)nickel. 

DFT calculations indicate that the oxidative addition reactions of a G-F bond in GeFe at Ni(H2PGH2GH2PH2) and Pt(H2PGH2GH2PH2) proceed initially via exothermic formation of an 77 -arene complex. The G-F oxidative addition reaction is more exothermic at nickel than at platinum. The barrier for exothermic oxidative addition is higher at Pt than at Ni because of strong d-p repulsions in the transition state. Similar repulsive interactions lead to a relatively long Pt-F bond with a considerably lower stretching frequency in the oxidative addition product than for... 

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